Environmental, health, and safety concerns have prompted changes in the coating and ink industries from solvent based systems to water based systems. In addition, the high costs of solvents and the desires to minimize the quantity of petroleum based organic solvents in such systems have encouraged attempts to discover and develop new ink and coating systems based solely on water as the carrier or solvent. The production of water based systems has also been encouraged by the increasing government restrictions imposed on the user on the amounts and types of organic volatiles permitted to escape into the atmosphere.
Known are three general types of polymers used in water-borne systems, soluble, semi-soluble and latex. The soluble polymers are characterized by clear solutions, whose viscosity depends on the molecular weight of the resins. They are generally made in solution and diluted with water to achieve the desired viscosity for proper application. Thus, they generally have a higher solvent or water content than do the latex compositions. The latexes, in contrast, are opaque suspensions of polymer particles, generally less than one micron in size. The viscosity of a latex is dependent on particle packing rather than one molecular weight and, as a consequence, a combination of high molecular weight and low viscosity at relatively high solids can readily be obtained. The semi-solubles, also called colloidal dispersions, are translucent in appearance and are generally characterized by properties intermediate of those possessed by the solubles and the latexes.
Water-soluble vehicles are of interest and often preferred in place of latex composition because they generally exhibit better flow properties, better pigment binding, and higher gloss of the cured coating.